gingeRS Here's a good thread that I searched for in which oilman explains what are the best oils to use on your Cosworth in his opinion (and also alot of other peoples).
My picks for oil, there would be only 2 brands.

https://passionford.com/forum/viewtopic.php?t=140172

Silkolene Pro R 15w-50, Silkolene Pro S 10w-50

http://www.opieoils.co.uk/performanc...silkolene.aspx

Motul 300V Competition 15w-50

http://www.opieoils.co.uk/performanc...nts/motul.aspx